[vsnet-chat 787] about SN 1998T; positions, identifications and magnitudes

[Yamaoka Hitoshi <yamaoka@rc.kyushu-u.ac.jp>]

Dear Drs.,

  There seems to be some confusions about the position and 
identification of recently appeared SN 1998T. Below is my
present understandings. 

  The object at the position reported by Balam (IAUC 6844) is also
seen in Digitized Sky Servey 2 image. It should be a knot of IC 694. 
B-band image on http://vsnet.ifa.hawaii.edu/postdocs/vacca/images/
arparp299buv.html shows faint glow on this position. The R-band image
taken on 1998 Mar. 18.5 UT with 0.95-m reflecter by Michinari
Yamamoto, Ayabe Astronomical Observatory, Japan shows very faint knot 
(R ~ 17 mag) on this position. 

  The position (accuracy ~ 1 arcsec; from GSC coordinate) of 
stellar-looking object which lies the southern side of the dust lane
of IC 694 (cf. Filippenko and Moran, IAUC 6430) derived from Ayabe
image is: R.A. = 11h28m33s.1, Decl. = +58o33'44" (2000.0). I have
sent this image to Dr. Filippenko, and he agreed that this point is
the SN 1998T. This image can be seen at:
http://vsnet.obs.misato.wakayama.jp/~ayabe/michi/ayabe.jpg .

  The position of the nearby star mentioned by Balam (IAUC 6844) 
derived from Ayabe image is estimated as 34s.1, 31'22" (end
figures), which is consistent to Balam's position. Comparing to this 
star (R = 17.3), GSC 0383100688 is R = 15.0 and GSC 0383100549 is 
R = 15.1. The brightness of stellar-looking knot is uncertain because 
it is overlying the bright region of the host galaxy, but it probably 
is not brighter than R = 16. 

  It seems that the visual magnitude estimates reported on IAUC (or
other places) are inconsistent with this R magnitude. I guess a part
of observers are studying the other object. Among these reports, Dr.
Howerton (e-mail: hwcomdso@horizon.hit.net) mentioned that he has been
observing the object on the northern half of the southwestern galaxy,
which is identified as NGC 3690 according to Wynn-Williams et al.
(1991). And he mentioned that this object has been rapidly dimmed
between Mar. 21 UT to 26 UT. His visual estimates are: 
  980321.251   130  (S. Howerton)
  980322.222   135  (S. Howerton)
  980325.149   139  (S. Howerton).
If this decrease is real, there should be another SN on the same time.
It is very rare case, but not exclusive. 

  And, on DSS2 image, there is a stellar-looking object in IC 694, 
which does not exist in the current images; which is about 17 mag and 
the position is 11h28m33s.5, 58o33'32". This image has taken on 1993
Apr. 22, so it should be identical SN 1993G. It is noticed on IAUC as 
"SUPERNOVA 1993G in NGC 3690", but this position shows that this SN
was appeared on the same galaxy (IC 694) as SN 1998T. This discrepancy
was first noticed by T. Kato, Kyoto Univ.. As Kato mentioned, there
must have been histrical confusions that which part of Arp 299 is
NGC 3690/IC 694. 

Sincerely yours,
Hitoshi Yamaoka, Kyushu Univ., Japan
yamaoka@rc.kyushu-u.ac.jp

VSNET Home Page

Return to Daisaku Nogami

---

vsnet-adm@kusastro.kyoto-u.ac.jp